1. Field of the Invention
This invention relates to a method for making porous refractory materials.
2. Description of the Prior Art
Refractory material having numerous permeable pores has been widely used in the steel making industry and in other fields.
For instance, refractory material having a large number of permeable pores is conventionally manufactured by mixing powder of a highly refractory material having a controlled grain size with binding clay or an organic binder and then forming it under pressure, followed by drying and baking. The cavities produced within the brick provide permeability. However, such pores do not have directionality. Because of this lack of directionality, the pores are present in directions other than one specific certain direction and are of no use of the passage of gas and, instead, are markedly detrimental to the corrosion resistance, for instance, in the case of porous plugs for the gas bubbling of molten metal. Further, it is practically impossible to control the size of the pores in this manufacturing method without the sacrifice of refractoriness, abrasion resistance, strength, and other desired properties.
Another prior art process is shown in U.S. Pat. No. 3,060,015, in which a molded plate is bored with numerous needles and then dried and baked. A manufacturing method of such refractory material is disclosed in Japanese Patent Publication No. Sho 38-26836. The method of this Japanese patent publication is such that a number of needle-like holes are bored by passing needles (of various forms) through an original plate made of molding material by press molding, and then drying and baking.
In this method, however, the plate strength determines the size of the bores and, accordingly, small pores are difficult to obtain. Another disadvantage of this method is that the through pores are closed if an external force acts on the plate. Also, needles are passed through the original plate and the size of the needles is determined by the strength of the original plate and, accordingly, minute pores are difficult to form. Moreover, if an external force is applied by chance to the original plate having many holes before drying, permeable holes are blocked and closed. Accordingly, the manufacturing method must be free from external force, such as, vibration.
Another method is disclosed in U.S. Pat. No. 3,539,667, in which combustible fibrous substances are disposed in the molding flask and a slurry of refractory material is filled into the mold, and then dried and baked. In this method, an incombustible substance, for instance, wire, is introduced and taken out before baking. Specifically, a refractory material in slurry state is filled in a mold with combustible fibrous material arranged in a prescribed direction fixed thereto, removed from the mold, followed by drying and baking, so that permeable pores are obtained by combustion of the combustible matter.
U.S. Pat. No. 2,506,244 discloses the method of adhering a ceramic mass to a network of wooden rods and wefts to form a cylindrical body by winding said network and to dry and fire said body to obtain through pores corresponding to said wooden rods. The feature of this method is to produce a cylindrical body of ceramic material provided with narrow passages, parallel to the axis of said body. However, since wooden rods are used, it is difficult to produce extremely narrow passages.
In another method, through pores are obtained by filling a raw material in a molding flask provided with disposed incombustible material therein, such as, for example, wire, which is taken out before baking.
These methods, however, have the drawback that with the finer fiber or wire, the arrangement of fiber or wire becomes more complicated. Thus, in these manufacturing methods, as the fiber or wire becomes thinner, the work involved in arranging the fiber or wire becomes more complicated. The number of fibers or wires per unit area is extremely limited and, accordingly, the size of the fiber (or wire) must be relatively large in order to provide the brick with the desired permeability.
Accordingly, in the conventional manufacturing method of refractory material having a number of permeable pores extending in one direction, it is difficult to arbitrarily control the number of pores per unit area and the size of the pores and it is practically impossible to provide minute pores in a large number.